Re: How the concentration of sugar affects the respiration in yeast

sort of, but only under specific conditions.  let me explain.

when you say respiration, i assume you are talking about utilization of
oxygen, production of carbon dioxide and ethanol - and that goes along with
other metabolic functions, cell division, etc.

let's look first at a human - let's suppose a child needs three meals plus
2 snacks a day in order to maintain good health and a good growth rate.  a
child won't necessarily grow faster if i kept offering it food 10 times a
day, right?  (it might get fat, but it won't get taller any faster.)  on
the other hand, i might stunt a child's growth if i only offerred it food
once a day, or once every other day.

now how does this apply to yeast?  like a child, a single wild yeast cell
only needs so much air, so much nutrients, etc. for it to live happily and
well and produce offspring.  (think of respiration as being a part of
living happily.)  if i give it surplus concentrations of sugar, will it
necessarily grow faster, divide more frequently, and respire more?  no, of
course not.  however, if i am starting it off in starving conditions (ie
*no* sugar), and start increasing the sugar concentration, you will see a
rise in respiration, rise in metabolism, etc.  only under this circumstance
is the answer to your question "yes."

if you take it *too* far and add way more sugar than necessary, you can
induce something called osmotic shock.  let's say you have a sugar solution
so thick that it has a consistency more like jelly than like water.  if you
put yeast in it, the high concentration of sugar will pull the water out of
the yeast cell, through the membrane and cell wall, effectively dehydrating
the yeast.  (you might have done something similar using a carrot and
saltwater, maybe in grade school - over time, the carrot shrivels, even
though it is submersed.)  this dehydration principle is why things like
fruit rollups or dried foods exist with minimal preservatives - without
enough water, microorganisms like yeast and bacteria cannot grow.

and, just for completeness, standard laboratory conditions for growing
yeast typically include 2% dextrose.  oh, and a lot of other things can
affect respiration in yeast - growth temperature, osmotic pressure (from
salts as well as sugar), ethanol concentration, the number of cells/ml, and
much more.

hope this helps
-j.